Electric protective device.



No. 729,236. PATENTED MAY 26, 1903.

C. P. STEINMETZ. I ELECTRIC PROTECTIVE DEVICE.

APPEIOATION FILED NOV. 16, 1901.

N0 MODEL.

WiGnessesH Inventor. fi-

M. Charles PSGeinmeCz.

" A by Am LII UNITED STATES Patented May 26, 1903.

PATENT OFFICE.

CHARLES P. STEINMETZ, OF SOIIENEOTADY, NEW YORK, ASSI'GN OR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTRIC PROTECTIVE DEVICE.

SPECIFICATION forming part of Letters Patent No. 729,236,. dated May 26,1903.

Application filed November 16, 1901. Serial No. 82,555. (No model.)

To all whom it may concern.-

Be it known that 1, CHARLES P. STEINMETZ, a citizen of the UnitedStates, residing at Schenectady, county of Schenectady, State of NewYork, have invented certain new and useful Improvements in ElectricProtective Devices, of which the following is a specification.

My present invention relates to a protective means for electriccircuits, and is particularly useful in connection with systems in whicha constant current is derived from a constantpotential circuit. Theinvention is of course valuable in connection with other systems thanthat mentioned.

In the appended claims I have pointed out the novel features which Ibelieve characterize my invention. The details of construction and modeof operation of apparatus embodying the invention will, however, be moreclearly understood by reference to the following description, taken inconnection with the accompanying drawings, in which Figure 1 is adiagram of one embodiment of my invention, and Fig. 2 is a diagram of amodification.

The system shown in Fig. 1 is one in which the constant-current circuit1 is derived from a source of constant-potential current 2 through theinteraction of lagging and leading currents produced by reactances ofopposite sign-that is, reactances in the nature of inductances andcondensers. Arrangements embodying the use of reactances of oppositesign for changing constant-potential current into current of constantvolume are known in the art, and one of these is shown in Fig. 1 forpurposes of illustration. The arrangement thus shown consists of acompensator or similar winding 3, across the terminals of which asubstantially constant electromotive force is maintained bytheconstant-potential source 2 of alternating current. Acondenser 3 and aninductance-coil 4 are connected in series with each other across theterminals of the winding 3, as shown. The constant-current circuit 1 hasone terminal connected to the junctionbetween thecondenser and theinductance-coil andits other terminal to the middle point of the winding3. If the values of the condenser and inductance be chosen to correspondto the condition of resonance for the particular frequency of thecurrent supplied from the alternating-current source 2, it will be foundthat the current in the circuit 1 will be constant, regardless of theresistance of this circuit. Inasmuch as my invention does not relate tothe specific means for producing a constant current, no furtherexplanation of the theory of action of the device shown is believed tobe necessary.

In order to provide against the injurious effect of continued opencircuit of the 0011- stant-current mains in case the same should happenaccidentally or otherwise, I make use of an arrangement which preventsan absolute cessation of flow of current in the constantcurrent circuit,and in conjunction therewith I employ means operating in a suitablemanner either to short-circuit the constant-current circuit oropen-circuit the constant-potential circuit. Fig. 1 shows the apparatusarranged to open the constant-potential circuit.

The protective device shown in Fig. 1 consists of a spark-gapdischarge-circuit 5 across the constant-current mains 1, this spark-gapcircuit being operatively related to a circuitbreaker 6 in one of theconstant-potential mains leading from the source of current 2. Thespark-gap circuit includes a suitable number of balls or otherconducting-pieces 7 arranged in a series and separated from each otherby suitably-proportioned gaps. This series of balls is included in acircuit across the constant-current mains, Which circuit may alsoinclude a small resistance 8 sufliciently large to prevent theoccurrence of electrical oscillations, together with a solenoid 9 foractuating a circuit-closing device 10. This circuit-closing device acts,when operated, to close a local circuit, including a source of current11 for energizing the tripping-coil 11 of the circuit-breaker 6 for oneof the constant-potential-supply mains. In stead of using this relayarrangement for operating the circuit-breaker 6, it is of course obviousthat any other suitable arrangement might be employed. Thus the solenoid9 might, if desired, operate directly as the tripping-coil for the saidcircuit-breaker. I

It is undesirable that a momentary discharge through the spark-gapcircuit should operate to trip the circuit-breaker '6. I thereforeemploy a time-limit device which acts to delay the tripping of thecircuit-breaker until the discharge in the spark-gap circuit shall havecontinued for a time. The arrangement shown consists of a fuse 11connected in shunt to the solenoid 9 and located so as to be within theinfluence of the stream of hot air or gas produced by the discharge ofcurrent across the sparkgaps of the spark-gap circuit. To render theheating effect of the discharge across the spark-gaps more effective, Iplace the spark-gaps within a chamber provided with an opening acrossthe mouth of which extends the fuse referred to. The inclosing box orenvelop for the spark-gaps is indicated in the drawings at 12 and thedischarge-opening therein at 13. The fuse 11 will be seen mounted acrossthis dischargeopening. XVhenever the discharge continues for asufficient length of time, it will be evident, therefore, that the fusemay be heated sufficiently so that, in conjunction with the heatproduced by the current traversing the same by reason of its shuntconnection to the solenoid f), it melts, thereby causing the totalcurrent of the spark-gap circuit to pass through the solenoid, whichlatter then acts to close the local circuit and operate thecircuit-breaker in the constant-potential circuit. The carrying capacityof the fuse is slightly greater than that necessary to enable the fuseto carry its share of the current in the circuit, and the fuse thereforemelts or blows only if the discharge of current across the gaps betweenthe conducting-pieces 7 continues a length of time sufficient to reducethe carrying capacity to the melting or blowing point. Fig' 2 shows asomewhat different protective device applied to a system of the samecharacter as in Fig. 1. As in Fig. 1, a circuitbreaker is shown asoperatively related to one of the constant-potential mains. Thiscircuit-breaker, however, is arranged so as to respond to minimumcurrent in the constantpotential mains and not to an overload. Anysuitable circuit-breaker thus operating may be employed. In the drawingsI have represented a circuit-breaker in which the trippingarm, unlikethat of the usual circuit-breaker, is acted upon by a spring 14, tendingto trip the circuit-breaker, and a coil 15 in series with one of themains tending to hold shut the circuit-breaker. WVhenever the current becomes sufficiently small, the spring 14 overpowers the action of thecurrent in the coil 15, and thereby trips the circuit-breaker.

Across the constant-current circuit I connect the discharge-circuit,consisting of aplu rality of discharge-terminals or balls 16, in serieswith which is a resistance 17, having a negative temperaturecoefficient. This resistance may be formed of magnetite or some similarsuitable substance. 111 case abnormally high Voltage is impressed uponthe constant-current circuit, as would be the case if the circuit wereaccidentally or otherwise ruptured, a discharge will take place betweenthe discharge-terminals 16. This flow of current will act not only toreduce the abnormal voltage on the lines, but will cause the resistance17 to be heated. As the latter rises in temperature its resistancedecreases, thereby causing the impressed voltage of the constantcurrentcircuit to decrease. As the voltage of the constant-current circuitdecreases the current in the constant-potential circuit likewisedecreases. A point is finally reached when the current in the coil 15 ofthe circuitbreaker in the constant-potential mains is no longer able tohold the circuit-breaker closed. The constant-potential-supplycircuit istherefore opened. The resistance 17 is chosen of such value that whentraversed by current through the discharge circuit it will when coldimpose such a load upon the constantcurrent circuit as will make thecurrent in the constant-potential-supply circuit high enough to maintainthe circuit-breaker in the latter circuit closed, while when hot it willre duce the load enough to cause the circuitbreaker to open. The delaywhich takes place before the resistance can become heated enough toreduce the voltage in the constantcurrent circuit sufficiently, and byconsequence the current in the constant-potential circuit, operates asthe time element in the control of the said circuitbreaker. By shapingthe resistance so as to have a greater or less radiating-surfacerelative to its volume the time interval may within limits be adjustedas desired.

Vhat I claim as new, and desire to secure by Letters Patent of theUnited States, is

1. The combination of a constant-potential circuit, a constant-currentcircuit fed thereby, and a device responsive to voltage of theconstant-current circuit for opening the constantpotential-supplycircuit.

2. The combination of a constant-potential circuit, a constant-currentcircuit operatively related thereto, and a device for opening theconstant-potential circuit in response to an abnormal increase ofresistance in the constant-current circuit due to opening of the latteror to other causes.

3. The combination of a constant-potential circuit, a constant-currentcircuit operatively related thereto, a circuit-controlling device forthe constant-potential circuit, and means provided with a time limit andoperated from the constant-current circuit for controlling said device.

4. The combination of dependent circuits, one carrying a normallyconstant current and the other a variable current, and means responsiveto abnormal voltage in the circuit carrying the constant current forinterrupting the circuit carrying the variable current.

5. The combination of a constant-current circuit, a discharge-circuitacross said 0011- stantcurrent circuit, said discharge-circuit includingone or more gaps, and a fusible conductor in shunt to a portion of saiddischargecircuit and located in proximity to said gap or gaps.

6. The combination of a plurality of conductors arranged so as to form agap or a series of gaps, and a fusible conductorarranged so as to betraversed by current passing across said gap or gaps and located inproximity to said gap or gaps.

7. The combination of spark-gap terminals, an inclosure therefor, anopening in said inclosure, a thermal cut-out in proximityto saidopening, and an electric circuit including said cut-out. p

8. The combination of spark-gap terminals, an inclosure therefor, anopening in said inclosure, and a fuse in proximity to said opening andin circuit with said terminals.

9. The combination of terminals between which an arc may be formed,means for confining the fioW of hot air or gases due to such'

